1. Field of the Invention
The present invention relates to a process for synthesizing trimethyl-p-benzoquinone from trimethylphenol and, more particularly, it relates to a process for producing trimethyl-p-benzoquinone in high yield by introducing a halogen group to p-position of 2,3,5- or 2,3,6-trimethylphenol and oxidizing the resulting 2,3,5- or 2,3,6-trimethyl-4-halogenophenol.
2. Description of the Prior Art
As has already been well known, trimethyl-p-benzoquinone is readily reduced to trimethylhydroquinone, which is important as a starting material for synthesizing vitamin E.
There have heretofore been various literatures and patents as to the process for producing trimethyl-p-benzoquinone by oxidizing trimethylphenol. For example, there is a description in "Journal of Organic Chemistry", 4, 318(1939), that trimethyl-p-benzoquinone is obtained in 50 percent yield by oxidizing trimethylphenol with chromic acid in an aqueous sulfuric acid solution. Furthermore, in this literature, trimethylphenol is diazotized with a diazotizing solution and hydrogenated to produce trimethyl-p-aminophenol, which is then oxidized with ferric chloride to obtain trimethyl-p-benzoquinone in 95 percent yield. However, the above-described processes are economically disadvantageous since many steps are involved and expensive chemicals are used.
Also, in the process described in Japanese Pat. Publication No. 38063/70 (German Pat. OLS No. 1,814,652), 2,3,6-trimethylphenol is dissolved in acetic acid and oxidized with a dilute nitric acid using sodium nitrite as a catalyst to obtain trimethyl-p-benzoquinone in maximum yield of 69.6 percent. This process is simple and is considered to be a good one. However, the yield is a little low.
Various oxidizing processes are under examination also in other literatures. However, there are produced in many cases a diphenoquinone-homolog product and the selectivity to the desired trimethyl-p-benzoquinone is low.